‘Impossible’ Cloud on Titan Explained Cloud crystals in the super-cold environment of Titan are revealing surprising solid-state chemical processes that illuminate similar chemistry occurring in Earth’s polar stratospheric clouds. Titan’s spring brings polar ice clouds made of dicyanoacetylene (C4N2) molecules. The presence of these polar clouds seemed impossible, because Cassini infrared measurements showed there is not enough C4N2 in the stratosphere to form the observed ice clouds. So where does the C4N2 come from? Cassini found that springtime sunshine kicks off an ‘on-site’ manufacturing process that produces the icy raw material for the C4N2 clouds. Photochemical reactions between hydrogen cyanide (HCN) and cyanoacetylene (HC3N) in Titan’s stratosphere were found to produce C4N2 .This unexpected photochemical effect on icy solids explains how these Titan’s Icy Polar Clouds The cloud at right seemingly ‘impossible’ clouds form in Titan’s springtime polar contains HCN. Some stratosphere! other polar stratospheric clouds are made of Something similar occurs in Earth’s polar stratosphere, where dicyanoacetylene (C4N2) which is produced from solid-state chemistry involving chlorine is at the heart of ozone sunlight-driven processes loss in Earth’s atmosphere. Comparison of the atmospheres of occurring on frozen Earth and Titan informs us on the fundamental processes that organic particles. A similar process is seen in occur throughout nature. Earth’s stratosphere between gases and water Solid-state photochemistry as a formation mechanism for Titan's stratospheric ice particles. C4N2 ice clouds. C. Anderson, R. Samuelson, Y. Yung and J. McLain, Geophysical Research Letters, 43, 3088-3094, 2016. .